The invention relates to a device for encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, wherein the stream of databits of the source signal is divided into n-bit source words, which device comprises converting means conceived to convert said n-bit source words into corresponding m-bit channel words in accordance with a conversion of the Jacoby type, where m and n are integers, with m greater than n.
The invention also relates to a method of encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, wherein the stream of databits of the source signal is divided into n-bit source words, said source words being converted into corresponding m-bit channel words in accordance with a conversion of the Jacoby type, where m and n are integers, with m greater than n.
The invention further relates to a binary channel signal comprising a stream of databits, converted from a binary source signal comprising a stream of databits, wherein the stream of databits of the source signal comprises n-bit source words, the channel signal comprising m-bit channel words, each one of said m-bit channel words corresponding to one of said n-bit source words in accordance with a conversion of the Jacoby type, where m and n are integers, with m greater than n.
The invention further relates to a record carrier comprising a binary channel signal comprising a stream of databits, converted from a binary source signal comprising a stream of databits, wherein the stream of databits of the source signal comprises n-bit source words, the channel signal comprising m-bit channel words, each one of said m-bit channel words corresponding to one of said n-bit source words in accordance with a conversion of the Jacoby type, where m and n are integers, with m greater than n.
The invention further relates to a device for decoding a stream of databits of a binary channel signal into a stream of databits of a binary source signal, wherein the stream of databits of the channel signal is divided into m-bit channel words, which device comprises deconverting means conceived to deconvert said m-bit channel words into corresponding n-bit source words in accordance with a deconversion of the Jacoby type, where m and n are integers, with m greater than n.
An encoding device and a decoding device mentioned in the foregoing are known from U.S. Pat. No. 4,337,458 (Jacoby channel code). The document discloses a device for encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, satisfying a (1,7) runlength constraint. This means that, in a serial datastream of the channel signal, minimally one xe2x80x98zeroxe2x80x99 and maximally seven xe2x80x98zeroesxe2x80x99 are present between two consecutive xe2x80x98onesxe2x80x99 in the channel signal. In this respect it should be noted that, normally, an additional preceding step is applied to the (1,7) constrained sequence, resulting in a runlength-limited sequence with a minimum runlength of 2 and a maximum runlength of 8.
The Jacoby channel code as such allows no DC-control at all. All conversions from source bits to channel bits are unambiguous. DC-control implies the reduction of the power of the channel bit stream near zero frequency. The spectral notch at DC allows retrieval of the threshold level from the detected waveform, which is essential for timing-recovery with the PLL.
It is an object of the invention to provide an improved device for encoding n-bit source words into corresponding m-bit channel words in accordance with a conversion of the Jacoby type, so that DC-control is made possible.
The encoding device in accordance with the invention is characterized in that the device further comprises control means for carrying out DC-control on said binary channel signal by introducing a freedom of choice in the source-to-channel conversion.
The invention is based on the recognition that DC-control will be made possible by introducing an appropriate freedom of choice in the source-to-channel conversion. Therefore, two options in the choice for some predetermined source-to-channel conversions are created. Both options are different in one extra xe2x80x981xe2x80x99 in the channel stream of databits in NRZI-notation, so the difference is one extra transition in the channel stream of databits, which has the effect of transforming the pit-bits into land bits (or marks and non-marks in the case of phase change recording) and vice versa after the extra transition. Due to this extra transition, the so-called running-digital sum (RDS) value can be kept within certain bounds, which is a sufficient condition for the generation of a spectral notch at DC. This kind of DC-control will be referred to as stochastic DC-control. The RDS gives a measure of the low-frequency content as it is defined as the difference between the totals of pit and land lengths in the channel stream of databits.
In the parity preserve channel code, e.g. described in U.S. Pat. No. 5,477,222 (PHN 14448), DC-control is also performed by limiting the RDS within certain bounds. The main difference with the parity preserve principle is that the latter needs extra bits, the so-called parity preserve bits, before the channel encoding operation in order to control the RDS value. In this invention, no extra bits are needed, since the bits that allow control of the RDS value are implicitly present in the source-to-channel conversion with double options. The frequency of occurrence of these DC-control points in the channel bitstream depends on the actual content of the source bitstream, which makes the type of DC-control in this invention to be of a stochastical nature. This invention has as an advantage that the capacity of a record carrier can be enlarged.
The encoding device in accordance with the invention is characterized in that the device further comprises bit-adding means for carrying out additional DC-control.
The encoding device in accordance with the invention is suitable to be included in the encoding arrangement, where merging bits are inserted after every q bits in a serial channel bitstream in order to realize an extra DC-control. This may be suitable if the stochastic DC-control as introduced before is regarded to be insufficient.
The purpose of the bit-adding means is to add bits to the channel bitstream, so as to obtain a precoder output signal in which the power of the channel bitstream near zero frequency is further reduced, improving the DC-control. The added bits that are present in the channel bitstream are usually referred to as merging bits. The precoder output signal is recorded on a record carrier. The addition of an n-bit code word to the consecutive code words allows a change of the sign of the RDS contribution.
The method in accordance with the invention is characterized in that the method further carries out DC-control on the binary channel signal by introducing a freedom of choice in the source-to-channel conversion.
The signal in accordance with the invention is characterized in that, in said binary channel signal, a pair of blocks of p consecutive m-bit channel words, being converted from the same block of p consecutive n-bit source words, is present, the blocks of the pair differing from each other in the bit value at one bit position only in said blocks, p being an integer which is larger than 1.
The record carrier in accordance with the invention is characterized in that, in said binary channel signal, a pair of blocks of p consecutive m-bit channel words, being converted from the same block of p consecutive n-bit source words, is present, the blocks of the pair differing from each other in the bit value at one bit position only in said blocks, p being an integer which is larger than 1.
The decoding device in accordance with the invention is characterized in that said deconverting means are also conceived to deconvert a channel sequence comprising pairs of blocks of p consecutive m-bit channel words into the same blocks of p consecutive n-bit source words, the pairs of blocks of p consecutive m-bit channel words differing from each other in the bit value at one bit position only in said blocks, p being an integer which is larger than 1.
With this device, the binary data signal according to the invention, comprising a stream of databits, can be deconverted into a binary source signal comprising a stream of databits.